Violent kinematics in the Lyα nebula of BR1202-0725. Top left: integrated spectra of regions with negative (blue curve) and positive (red curve) velocity shifts for BR1202-0725, with respect to the peak of the nebular Lyα emission (see Fig. 2). The spectra are taken after masking the 1″ × 1″ region of the QSO’s PSF-subtraction and a circular region with a diameter of 1.6″ at the LAE companion position. We indicate with vertical lines the systemic redshift (solid magenta), the redshift of the SMG (dashed black), and LAE (dot-dashed green) companions (Carilli et al. 2013; Drake et al. 2020). Top middle: residual spectrum between the positive and the negative shift spectrum. We indicate the systemic redshift with a magenta line. Top right: Lyα velocity shift map computed from the first moment using a spectral window of ±FWHM centered at the peak of the nebular Lyα emission (see Table 3) and smoothed as in Fig. 2. The position of the QSO and LAE companion masks are indicated with a hashed gray and a green circle, respectively. Bottom left: Lyα SB map using the spectral channels with the largest negative nebula shifts, indicated with a blue shaded region in the top-left panel. The blue contours indicate the 2σ isophote of the extended emission shown in Fig. 2. Bottom right: Lyα SB map using the spectral channels with the largest positive nebula shifts, indicated with a shaded red region in the top-left panel. Both of the SB maps are smoothed at the bottom as in Fig. 2. All maps have a side of 20″ and black contours indicating SB levels of [2, 4, 10, 20, 50] σ within the respective wavelength ranges.